In general, the pneumatic tire comprises a belt comprised of at least two cross belt layers, reinforcing elements embedded in which layers being crossed with each other with respect to an equatorial plane of the tire. In JP-A-2000-203215 is disclosed a pneumatic tire wherein at least one belt reinforcing layer having a width wider than that of the belt layer, in which plural reinforcing elements are embedded therein so as to extend in a circumferential direction while bending in wavy or zigzag form, is further provided for controlling separation failure at a widthwise outer end portion of the belt layer to improve a belt durability.
However, an outer surface of a tread portion in the pneumatic tire including the tire disclosed in the above publication is generally constructed with an arc having a single radius of curvature or a plurality of arcs having different radii of curvature for properly holding a ground contacting shape or a ground contact pressure, and shaped into a convex form increasing a radius (distance from a rotating axis) from both tread ends toward the equatorial plane of the tire.
When the outer surface of the tread portion is shaped into the convex form as mentioned above, there is a problem that irregular wear is caused because a force directing forward in a traveling direction (driving side) in the vicinity of the equatorial plane of the tire and a force directing backward in the traveling direction (braking side) in the vicinity of the tread end are applied to the outer surface of the rotating tread portion in accordance with a size difference (difference in peripheral length) to increase a wearing rate at the tread end portion. Such a problem or wearing at the tread end portion becomes more remarkable when the pneumatic tire is particularly mounted onto a driving wheel of a vehicle because the backward force becomes larger.
Now, the inventor has made various studies with respect to a wear generating mechanism in the tread end portion of the pneumatic tire disclosed in the above publication and obtained the following knowledge. That is, as shown in FIG. 10, when the force directing forward in the traveling direction is applied to the vicinity of the equatorial plane of the tire and the force directing backward in the traveling direction is applied to the vicinity of the tread end during the rotation of the tire, the tread portion is subjected to shearing deformation. Even when widthwise outer end portions of one or more of widest-width belt reinforcing layers are existent outside a widthwise outer end of a wider-width belt layer in the widthwise direction, since the embedded reinforcing elements extend substantially in the circumferential direction and shearing rigidity in the circumferential direction at the outer end portion of the belt reinforcing layer is small, the shearing deformation becomes violently large at the tread end portion corresponding to the above outer end portion and hence a large slippage to a road surface is always generated and the wearing rate at the tread end portion becomes large.